Scientists create 3D printed wearable sensors for plants, enabling measurements of water use in crops

Jan 5, 2018 | By Benedict

Scientists at Iowa State University are using 3D printing to make graphene-based sensors-on-tape that can be used to collect data about water use in crops. The sensors could also be used in biomedical diagnostics, architecture, and other fields.

With a technology that can produce precise patterns of graphene as small as 5 millionths of a meter wide, you might wonder why Iowa State University is using such technology to produce “tattoo sensors” for plants.

The answer lies in data collection. By attaching graphene-based sensors-on-tape to plants, Iowa State scientists can provide new kinds of data to researchers and farmers, helping them better understand the natural processes behind plants and taking advantage of that knowledge to produce better results—academic or commercial.

“With a tool like this, we can begin to breed plants that are more efficient in using water,” says Iowa State plant scientist Patrick Schnable. “We couldn't do this before. But once we can measure something, we can begin to understand it.”

The tiny plant sensor is made from graphene, an atom-thick form of carbon that is strong and stable and a great conductor. It’s a highly useful material, but one that’s relatively hard to manipulate, which means scientists are constantly looking for new ways to make the most out of the material.

The Iowa State researchers have attempted to produce intricate graphene patterns on tape, and have done so with the help of 3D printing.

The process starts with one of the scientists making indented patterns on the surface of a polymer block, either using a 3D printer or a molding process. This provides the starting point. Next, a liquid graphene solution is applied to the block, filling the indented patterns like water running through canals.

Excess graphene can then be removed with tape, before another strip of tape is used to precisely remove the graphene patterns from the block. The end result is a strip of tape complete with a complex 3D printed graphene pattern.

It’s a process that can result in high-resolution graphene arrangements. Patterns as fine as 5 millionths of a meter wide, or one-twentieth the width of a human hair, can be made using the process, resulting in sensors with a high level of sensitivity.

It’s also a highly affordable process, which could make it appealing to a variety of users: “This fabrication process is very simple,” says Liang Dong, associate professor of electrical and computer engineering at Iowa State and lead author of the paper. “You just use tape to manufacture these sensors. The cost is just cents.”

When making the sensors for plants, the researchers use graphene oxide, which is highly sensitive to water vapor, changing its conductivity in response to the presence of water vapor. This means the sensors can be used to accurately measure the transpiration (release of water vapor) from a leaf.

The stick-on plant sensors have been successfully tested in lab and pilot field experiments, and could be developed much further if the research group receives a patent for the sensor technology. An option for the commercialization of the technology has also been agreed with EnGeniousAg, a startup involving some of the researchers.

The scientists are confident in the potential of the graphene sensors, which can be used for applications besides crop research. Biomedical diagnostics, checking the structural integrity of buildings, monitoring the environment, and testing crops for diseases or pesticides are all activities that could be improved with the technology.

For now, however, the researchers want to focus most of their energy on the plant sensors they have developed.

“The most exciting application of the tape-based sensors we've tested so far is the plant sensor,” Dong says. “The concept of wearable electronic sensors for plants is brand new. And the plant sensors are so tiny they can detect transpiration from plants, but they won't affect plant growth or crop production.”